This invention relates generally to a mask and an exposure method using the same. More particularly, the invention is concerned with a mask and an exposure method which can be suitably used in the manufacture of various devices such as semiconductor chips (e.g., ICs or LSIs), display devices (e.g., liquid crystal panels), detector elements (e.g., magnetic heads), and image pickup devices (e.g., CCDs), for example.
The manufacture of microdevices such as ICs, LSIs or liquid crystal panels, for example, use a projection exposure method and a projection exposure apparatus wherein a circuit pattern formed on a photomask or reticle (hereinafter, xe2x80x9cmaskxe2x80x9d) is projected through a projection optical system onto a photosensitive substrate such as a silicon wafer or a glass plate (hereinafter, xe2x80x9cwaferxe2x80x9d) which is coated with a photoresist, for example, by which the circuit pattern is transferred (photoprinted) to the wafer.
In such a projection exposure method and projection exposure apparatus which play a main role in wafer microprocessing procedures, many attempts have been made to improve the resolution and to enlarge the exposure area in order that an image (circuit pattern image) of a size (linewidth) of 0.5 micron or less can be formed in a wider range.
On the other hand, currently, projection exposure apparatuses having an excimer laser as a light source are used widely, because of its high projection resolving power. However, it is still difficult to produce a pattern image of 0.15 micron or less.
U.S. Pat. No. 5,415,835 shows a technique for forming a very fine pattern in accordance with dual-beam interference exposure. With this dual-beam interference exposure, a pattern of a linewidth 0.15 micron or less can be produced on a wafer.
The same assignee of the subject application has proposed in Japanese Patent Application Nos. H10-221095, H10-201333 and H10-221097 an exposure method by which, through a dual exposure process to a photosensitive substrate (to be exposed) including a periodic pattern exposure and an ordinary (standard) exposure, a circuit pattern having a portion of 0.15 micron or less can be produced.
Here, the term xe2x80x9cordinary exposurexe2x80x9d or xe2x80x9cstandard exposurexe2x80x9d refers to an exposure process by which an arbitrary pattern can be photoprinted although the resolution is lower than that of the periodic pattern exposure. A representative example of it is the exposure process to be performed by projection of a mask pattern with a projection optical system.
A pattern to be printed by the standard exposure (hereinafter, xe2x80x9cstandard exposure patternxe2x80x9d) may include a very fine pattern less than the resolution. The periodic pattern exposure is a process for forming a periodic pattern of a similar linewidth as that of the very fine pattern. Such a periodic pattern exposure may use a Levenson type phase shift mask, for example.
FIG. 23 is a schematic view for explaining a dual exposure process. A periodic pattern (A) and a standard exposure pattern (B) are printed, by dual exposure, on the same position, by which a combined synthetic pattern (image) (C) is produced. Details of the principle of multiple exposure will be described later.
FIG. 24 is a schematic view for explaining an inconvenience to be caused when a very fine pattern is formed through a dual exposure process using a periodic pattern and a standard exposure pattern. FIG. 24, at (A), shows the relation between first and second periodic patterns 1 and 2. FIG. 24, at (B), shows the relation between first and second standard patterns 1 and 2. FIG. 24, at (C), shows superposition of patterns by dual exposure. FIG. 24, at (D), shows the relation between first and second design patterns 1 and 2. FIG. 24 is an example wherein a pattern is to be formed in accordance with light transmitting portions, and the dual exposure process is performed so as to produce two design patterns (D) finally.
The standard exposure pattern shown at (B) in FIG. 24 may be analogous to the design pattern (D). Although it should be determined in light of the magnification of the exposure apparatus, in FIG. 24 it is illustrated with a simple magnification of 1.
The periodic pattern shown at (A) in FIG. 24 may be prepared in accordance with a very-fine line portion of the standard exposure pattern (B), and it may be made with the same pitch as a pattern being extracted only from the very-fine line portion of the standard exposure pattern. Thus, the periodic pattern (A), the standard exposure pattern (B) and the design pattern (C) in each set may have the same pitch.
The periodicity number of the periodic pattern (A) may be the same as or larger than that of the pattern being extracted from the very-fine line portion described above.
The shapes of the first and second periodic patterns 1 and 2 may be determined in accordance with the first and second design patterns 1 and 2. However, it has been found that, in dependence upon the spacing D between the first and second periodic patterns 1 and 2 which is determined in accordance with disposition of the design patterns 1 and 2, during the periodic pattern exposure process there may occur a disturbance in periodicity (i.e., disturbance of pattern) at the boundary between the first and second periodic patterns 1 and 2.
More specifically, it has been found that, if the pitch P1 of the first periodic pattern 1 and the pitch P2 of the second periodic pattern 2 differ from each other, there may occur a disturbance of periodicity at the boundary between the periodic patterns 1 and 2.
Also, even in a case wherein the pitches P1 and P2 of the design patterns 1 and 2 are equal to each other (P1=P2), in dependence upon a disposition of the design patterns, there may occur a disturbance in the periodic pattern. Now, an example of L=S where L is the width of lines and S is the width of spacings, both constituting the pitch of the periodic pattern, will be explained. If design patterns 1 and 2, wherein the design pattern spacing D is equal to a multiple of L or S by an odd number, are to be produced, the spacing D between the periodic patterns 1 and 2 is equal to the spacing width S and, therefore, no disturbance will be produced between the periodic patterns 1 and 2.
If, however, the spacing DS is made equal to a multiple of L or S by an even number, the spacing D between the periodic patterns 1 and 2 becomes D=2S. As a result of it, there occurs a disturbance in periodic pitch at the boundary between the two patterns. Further, also in a case where the spacing DS of the design patterns 1 and 2 is not equal to a multiple of S by an integer, the spacing between the periodic patterns 1 and 2 do not satisfy a relation D=S (which does not cause a disturbance in periodicity). As a result, there may occur a disturbance in periodicity.
As described above, since the periodic pattern should be determined in accordance with the design pattern and in light of current situations that patterns should be formed closely to each other, it is difficult to avoid a disturbance in periodicity, with the prior art, at the boundary between two adjacent periodic patterns in a periodic pattern exposure process, included in a multiple exposure procedure.
It is accordingly an object of the present invention to provide a mask and/or an exposure method by which disturbance of periodicity such as described above can be reduced significantly.
In accordance with a first aspect of the present invention, there is provided a mask for multiple exposures, having a plurality of periodic patterns in which a relation 0.5S less than D less than 1.5S is satisfied where S is the spacing between lines of a first periodic pattern of said plurality of periodic patterns and D is the spacing between the first periodic pattern and a second periodic pattern, of said plurality of periodic patterns, juxtaposed to the first periodic pattern with respect to the periodicity direction.
In accordance with a second aspect of the present invention, there is provided a mask for multiple exposure having a plurality of periodic patterns in which a relation 0.9S less than D less than 1.1S is satisfied, where S is the spacing between lines of a first periodic pattern of said plurality of periodic patterns and D is the spacing between the first periodic pattern and a second periodic pattern, of said plurality of periodic patterns, juxtaposed to the first periodic pattern with respect to the periodicity direction.
In a third aspect of the present invention, in relation to the first or second aspect thereof, adjoining pattern portions (lines or spaces) of the first and second periodic patterns juxtaposed with each other may have opposite phases.
In accordance with a fourth aspect of the present invention, there is provided a mask having a plurality of periodic patterns, wherein adjoining pattern portions (lines or spaces) of first and second periodic patterns of them, juxtaposed with each other, have opposite phases.
In accordance with a fifth aspect of the present invention, there is provided an exposure method including a process for exposing a photosensitive substrate to any one of the masks as recited above.
In accordance with a sixth aspect of the present invention, there is provided a multiple exposure method including a first exposure process using any one of the masks as recited above, and a second exposure process using another mask.
In accordance with a seventh aspect of the present invention, there is provided an exposure apparatus having an exposure mode for performing a process according to an exposure method as recited above, and a different exposure mode.
In accordance with an eighth aspect of the present invention, there is provided a device manufacturing method, characterized by an exposure process for exposing a wafer to a device pattern by use of an exposure method as recited above, and a developing process for developing the exposed wafer.
In accordance with a ninth aspect of the present invention, there is provided a mask having periodic patterns, wherein each of the first and second periodic patterns has a unit pitch defined by a line and a space, wherein the first periodic pattern has a first pitch P1 with a line width L1 and a space width S1 while the second periodic pattern has a second pitch P2 with a line width L2 and a space width S2, wherein the first and second pitches P1 and P2 are different from each other, wherein the first and second periodic patterns are juxtaposed with each other with respect to the periodicity direction, with a spacing D, and wherein, when one of the line widths L1 and L2 of the first and second periodic patterns is taken as L while one of the space widths S1 and S2 of them is taken as S, a relation 0.5Lxe2x89xa6Dxe2x89xa61S+0.5L is satisfied where L less than S is satisfied, whereas a relation 0.5Sxe2x89xa6Dxe2x89xa61L+0.5S is satisfied where Sxe2x89xa6L is satisfied.
In accordance with a tenth aspect of the present invention, there is provided a mask having first and second periodic patterns, wherein each of the first and second periodic patterns has a unit pitch defined by a line and a space, wherein the first periodic pattern has a first pitch P1 with a line width L1 and a space width S1 while the second periodic pattern has a second pitch P2 with a line width L2 and a space width S2, wherein the first and second pitches P1 and P2 are different from each other, wherein the first and second periodic patterns are juxtaposed with each other with respect to the periodicity direction, with a spacing D, and wherein the spacing D is equal to the space width S1 and/or the space width S2.
In accordance with an eleventh aspect of the present invention, there is provided a mask having a plurality of periodic patterns each having a unit pitch defined by a line and a space, wherein the plurality of periodic patterns include two periodic patterns having the same pitch and line width and being juxtaposed with each other with respect to the periodicity direction with a spacing D, and wherein, when the line width is L and the space width is S and when the spacing D is not equal to S, the spacing D is in a range which satisfies a relation 0.5Lxe2x89xa6D less than S or a relation S less than Dxe2x89xa61S+0.5L where L less than S is satisfied, whereas the spacing D is in a range which satisfies a relation 0.5Sxe2x89xa6D less than L or a relation 1S less than Dxe2x89xa6L+0.5S where Sxe2x89xa6L is satisfied.
In accordance with a twelfth aspect of the present invention, there is provided an exposure method including a process for exposing a photosensitive substrate to a mask as recited in relation to any one of the ninth to eleventh aspects of the invention described above.
In accordance with a thirteenth aspect of the present invention, there is provided a multiple exposure method including a first exposure process using a mask as recited in relation to any one of the ninth to eleventh aspects of the invention, and a second exposure process using another mask.
In accordance with a fourteenth aspect of the present invention, there is provided an exposure apparatus having an exposure mode for performing a process according to an exposure method as recited in relation to the twelfth or thirteenth aspect of the invention.
In accordance with a fifteenth aspect of the present invention, there is provided a device manufacturing method, characterized by an exposure process for exposing a wafer to a device pattern by use of an exposure method as recited in relation to the twelfth or thirteenth aspect of the invention, and a developing process for developing the exposed wafer.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.